This invention relates to an image forming apparatus equipped with an automatic both-side feed unit which can stack a plurality of paper sheets into a stacker, pick up the stacked sheets one by one in a reverse direction, and re-feed them with their surfaces reversed.
An automatic both-side feed unit incorporated in a digital copy machine is well known as a unit for automatically and continuously reversing a plurality of sheets of materials.
This both-side feed unit includes a stacker for temporarily containing sheets of, for example, paper, which each have one side passed through the image forming section of the machine and hence already provided with an image; a pair of side guides driven to repeatedly open and close to align both side edges of the paper sheets stacked in the stacker; a pickup roller for sequentially picking up the paper sheets, stacked in the stacker, beginning from the lowest one, in a reverse direction; and a paper re-feed conveyance path for sequentially re-feeding, to the image forming section, each paper sheet picked from the stacker by the pickup roller.
When forming images on both sides of each of a plurality of paper sheets by a copy machine with an automatic both-side feed unit as described above, at first, an image is formed on one side of each of all the paper sheets, using the image forming section, and then the paper sheets are sequentially stacked in the stacker. While stacking them, the side guides are driven each time five paper sheets are stacked in the stacker, so as to align the sides of the sheets. After all the paper sheets are stacked in the stacker, the side guides are closed and the pickup roller is rotated, thereby sequentially re-feeding the paper sheets to the image forming section, beginning from the lowest one. The image forming section sequentially forms a predetermined image onto the reverse surface of each re-fed paper sheet.
In order to enhance the productivity of the above-mentioned automatic both-side feed unit, forwarding control is executed in which the front end or ends of one or two paper sheets first stacked in the stacker are forwarded to the paper re-feed conveyance path located upstream of the image forming section. In this forwarding control, the pickup roller is rotated after one or two paper sheets are stacked into the stacker, thereby sequentially picking them up and feeding them to the paper re-feed conveyance path located upstream of the image forming section. This operation enables quick feeding of the front-end-forwarded one or two paper sheets to the image forming section when starting re-feeding of paper sheets which each have one side already provided with an image. As a result, the productivity of the automatic both-side feed unit can be enhanced.
Since, in this forwarding control, one or two paper sheets are once stacked in the stacker and then guided to the paper re-feed conveyance path, the forwarded position of the sheets on the re-feed conveyance path can be fixed. In other words, even when the one or two paper sheets are stacked at different speeds or at irregular points in time, the pickup pitch of the one or two paper sheets, and accordingly their forwarded position on the paper re-feed conveyance path, can be stabilized since the sheets are once stacked in the stacker and then picked up. The fixing of the forwarded position enables stabilization of the re-feeding operation of the first one or two paper sheets, and hence the productivity of the automatic both-side feed unit can be enhanced.
However, where the forwarding control, in which the front end or ends of first one or two paper sheets are forwarded to the paper re-feed conveyance path, is executed together with the control in which the side guides are driven each time five paper sheets are stacked in the stacker, the first one or two paper sheets are not aligned by the side guides when they are introduced into the stacker. Accordingly, the front end or ends of the first one or two paper sheets are forwarded to the paper re-feed conveyance path with unstable conveyance orientations.
More specifically, when a first paper sheet is guided into the stacker and then a second paper sheet is guided into the stacker and stacked on the first one, it is possible that the front end of the second sheet will hit the first sheet, thereby making the first sheet off-centered. Further, when a first sheet is picked up in a state in which a second sheet is stacked on the first sheet, and fed to the paper re-feed conveyance path, it is possible that the second sheet will be badly displaced. Thus, in the above-described conventional control, a paper sheet, which is forwarded to the paper re-feed conveyance path by forwarding control, will easily be displaced badly.
To prevent such a bad displacement of a first or second paper sheet picked up during forwarding control, it is considered to drive the side guides to align the first and/or second paper sheet picked up during forwarding control. However, if the side guides are driven to align the first and/or second sheet, it is possible that third to fifth paper sheets will be guided into the stacker when the side guides are closed, and hence that the third to fifth paper sheets will be brought into contact with the side guides and become jammed.
This invention has been developed in light of the above, and aims to provide an automatic both-side feed unit, which can reliably prevent a reversed paper sheet from becoming badly displaced, can execute forwarding control of stacked paper sheets, and hence has a high productivity, and also to provide an image forming apparatus equipped with the automatic both-side feed unit.
To attain the aim, there is provided an automatic both-side feed unit comprising: a containing section for containing, in a stacked manner, a plurality of sheets of materials sequentially introduced therein in a first direction; pressing means to be operated whenever each of the sheets is introduced into the containing section, to thereby press each sheet in a stacking direction; pickup means for picking up each sheet, introduced into the containing section, in a second direction opposite to the first direction; and aligning means to be operated when each sheet is in a released state assumed after each sheet is introduced into the containing section and before each sheet is pressed by the pressing means, the aligning means aligning each sheet together with other sheets already stacked in the containing section.
Further, an image forming apparatus according to the invention comprises: an image forming section for forming an image on one side of each of paper sheets; a containing section for containing, in a sequentially stacked manner, the paper sheets each having one side thereof provided with an image by the image forming section; introducing means provided near an inlet of the containing section for introducing the paper sheets each having the one side provided with the image which is formed by the image forming section, into the containing section in a first direction; pressing means to be operated whenever each of the paper sheets is introduced into the containing section, to thereby press each paper sheet in a stacking direction; pickup means for picking up each paper sheet, introduced into the containing section, in a second direction opposite to the first direction; paper re-feeding means for re-feeding each paper sheet picked up by the pickup means, to the image forming section; and aligning means to be operated when each paper sheet is in a released state assumed after each paper sheet is introduced by the introducing means into the containing section and before each paper sheet is pressed by the pressing means, the aligning means aligning each paper sheet together with other paper sheets already stacked in the containing section.